This glue is not the usual glue purchased from wood shops. It has additives in it to make it more adhesive to a wider variety of substances and to resist crazing when shrinking on external surfaces. One additive also gives it a slightly wider latitude of working time without affecting it’s strength.
It’s recommended that other additives are not used with this glue, as they can react with the present chemistry and seriously weaken it.
The hides used in this glue are no longer chrome-tanned. Therefore it is far better not to leave your pot on overnight and over weekends. Reheat the glue each time before using it. It must be reheated slowly to prevent breaking down the long protein chains that make strong glue. A microwave can be used if set less than 40% duty-cycle and as long as the glue never gets over 150 degrees.
Working time and glue consistency are the two most important things in using hot hide glue. In normal temperatures, when the work is not preheated, the glue must be spread (flowed on) evenly, thinly, and quickly and the parts placed smartly together. This requires thinning the glue for your type of brush and the surface to be glued. Beginners usually use too thick a glue.
If covering pneumatics, make sure that all end grain is pre-coated. If covering large bellows, always double glue, and then iron down the covers. When gluing down pneumatics, make sure the shelves have been sized with thin hot hide glue, first. Do not clamp pneumatics or anything on flat surfaces that might slide. Spring or C-Clamps cannot exert all their force at right angles to the bond plane and force some flat joints to creep, making a cold joint and an out-of-alignment part. Weights are the proper way to use force on flat bond surfaces.
Hot hide glue actually does not need a clamp. It grips by gelling. However, water in the glue will cause wood to sometimes warp a little. If you suspect that thin boards may bow a little as they get wet, size that board first and allow to air dry. Use only fresh glue for wood to wood joints.
Preheating wood parts to be glued is a good way to assure good joinery and pneumatic covers, by lengthening the active time that glue can be spread and contact can be changed or compressed. However it may not be possible to preheat the parts. In which case, even cold glue joints can be reheated, as long as they are fresh, and they will be restored. Adding water to glue slows setting.
In making wood to wood joints, leaving excess glue around a fresh joint makes it much more effective to reheat the joint for surety, since excess glue conducts heat rapidly into the joint. Usually a hair dryer is all that’s required. You can sometimes dampen the edges of the joint to aid this process. Remove excess glue then, after it has re-gelled and become semi-solid. Then use a wet rag or sponge and remove all traces of the glue. This is done so easily that the wood will stain exactly like the rest of the piece and there will be no telltale trace of glue on the surface.